In document distribution systems, the document to be transmitted is converted to millions of data bits per page. Document distribution systems may use coded information (CI) or non-coded information (NCI) to electronically send the document image. Whether the data is CI or NCI, it must be processed before it is transmitted. Processing may include data compression to reduce transmission time and data encryption for security purposes. Processing millions of data bits with a central processor to achieve these functions is wasteful and time-consuming.
Known techniques for improving data processing efficiency include time-sharing access by peripheral devices to a central processing unit (CPU) and time-sharing programs in a CPU. One example of such a system is taught in U.S. Pat. No. 3,029,414 issued to H. W. Shrimpf on Apr. 10, 1962. However, this system still processes all the data at the CPU and through the main memory. Therefore it does not lend itself to fast processing of large quantities of raw data from peripheral devices.
Another data processing technique is to time-share access to peripheral devices with two processing units. An example of this system is taught in U.S. Pat. No. 3,560,937 issued to R. P. Fischer on Feb. 2, 1971. The Fischer system could be adapted to handle vast quantities of peripheral data faster than the Shrimpf system simply because it can use two processors to attack the problem. However, all the data is still flowing through a single main memory and the processors at any one instant can only perform two functions since there are only two processors.
A technique for simplifying the access to peripheral devices is shown in U.S. Pat. No. 4,067,059 issued to N. Derchak on Jan. 3, 1978. In this patent the addressing of multiple peripheral devices is controlled by a "Shared Direct Memory Access" device. This does allow fast flexible simpler access to the peripheral devices, but all the processing is still performed by one CPU working with the memory. Accordingly, this system can not handle vast quantities of peripheral data any more efficiently than the Schrimpf system.
In the field of facsimile apparatus (NCI system), stored program control processors have been used to control a facsimile terminal as shown in R. E. Wernikoff et al U.S. Pat. No. 3,751,582. However, the control processing and the data processing both take place in the processor. Therefore, the system can not rapidly process vast quantities of video data without using an expensive and very powerful data processor.